Application Note AN-1077 - International Rectifier

Application Note AN-1077
In order to derive
chg
m
OCC PWM modulator. The control law is:
G
vˆ
Where M ( d ) =
vˆ
î
vˆ
we need to look at the
vˆ
m
⋅ RS
⋅î
(30)
g
M( d )
DC
=
g
o
g
vˆ = V + vˆ
(31)
in
in
The control to output for the constant power load
case is:
2
vˆ
o
Vin
vˆ
= 1
⋅
V ⋅ R ⋅G
sC
(35)
m
2
o
S
The power stage gain varies as expected with the
input voltage.
DC
ERROR AMPLIFIER: ( s )
o
H 2
The output voltage error amplifier in the IR1150
control IC is a transconductance type amplifier.
Substituting and eliminating the small signal cross
terms:
î
vˆ
g
m
V
V R G
in
= (32)
o
S
DC
40
20
Gain
0
20
Figure 13 - Error Amplifier
The transfer function is:
40
0.1 1 10 100 1 .10 3 1 .10 4 1 .10 5 1 .10 6
frequency
Figure 12 - Power Stage Gain @ 90V (red) and
265V (blue)
The output average current can be calculated from
the input current:
î
pˆ
î
⋅V
in chg o
g
= =
(33)
Vin
Vin
î
vˆ
chg
m
2
Vin
= (34)
V R G
2
o
S
DC
gm
⋅(
1+
sRgmCZ
)
H ( s ) =
(36)
2
s( C + C + sR C C )
Z
The compensation network shown on the schematic
diagram adds a zero and a pole in the transfer
function at:
f
P
gm
gm
1
f
Z
= (37)
0
2π
⋅ R ⋅ C
P0
=
2π ⋅ R
gm
Z
1
Cz ⋅Cp
Cz + Cp
Z
P
(38)
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